The-problem relates to the use of phenyl mercaptotetrazole (PMT) and derivatives in color paper photographic elements. While incorporation of PMT can be beneficial in reducing or eliminating cyan stain generated in developers contaminated by bleach-fix, it can also have a detrimental impact on what is termed "Wet Abrasion Sensitivity" (WAS).
The stain levels in color photographic paper prints vary with changes in the condition of the processing fluids in mechanical print processors. In particular, the cross-contamination of developer with bleach-fix can occur and causes increased stain. This stain is referred to as blix-induced stain. Color paper photographic elements which incorporate thiosulfonate addenda (for example, p-toluene thiosulfonate) to control heat sensitivity have been found to have an even worse blix-induced cyan stain problem.
We have found that the use of phenyl mercaptotetrazole (PMT) derivatives can reduce or eliminate the stain as long as the PMT or derivatives are added to the same layer as the thiosulfonate or are mobile enough to diffuse into the thiosulfonate containing layer from an adjacent layer. However, this solution is not always viable because of the Wet Abrasion Sensitivity concern, particularly in the magenta layer, described below.
Sometimes a plus or minus density mark is visible in the exposed region of a color print when pressure is applied to the emulsion in the first twenty seconds or so of immersion in the developer. This Wet Abrasion Sensitivity (WAS) problem is particularly acute for the magenta layer. We have found that the presence of phenyl mercaptotetrazole (PMT) in the magenta dispersion melts contributes to magenta layer WAS problems. PMT is used in the magenta layer to minimize "magenta dye streaking" but because of the WAS issue it would be preferable to remove it or replace it with a less mobile and a more hydrophobic derivative such as benzamidophenyl mercaptotetrazole (BAPMT). However, the removal of PMT or replacement by a addenda such as BAPMT in the magenta layer reintroduces the blix-induced cyan stain described earlier.
An obvious potential solution is the incorporation of PMT directly in the cyan layer. However, attempts to do this, either in the cyan dispersion or in the melt, have led to speed losses and melt hold stability concerns. Spectral sensitizers that are readily desorbed by competing addenda show larger speed losses than those red spectral sensitizers that are more tightly adsorbed to the grain surface.
U.S. Pat. No. 2,432,964 describes methods of making a solid particle dispersion of the AgPMT salt and also the photographic evaluation in which adverse effects on sensitivity are avoided and stain reduced, and U.S. Pat. No. 4,912,026 claims a combination of addenda, coupler solvent and gold sensitization.